1. Field of the Invention
The present invention generally relates to information storage apparatuses, and more particularly to an information storage apparatus which stores information by emitting a laser beam on a recording medium while a magnetic field is being applied.
Recently, optical discs have become a subject of attention as multimedia is being developed rapidly. It is desired for the optical discs to have an increasingly larger amount of storage. For example, a 3.5-inch MO has increased to a maximum of 1.3 GB. In order to achieve the large amount of storage, it is required to minimize a laser beam spot, to improve the accuracy of a focus servo, and to control the laser power accurately.
2. Description of the Related Art
In general, in a storage apparatus for use with a replaceable recording medium, the replaceable recording medium is mechanically displaced to a spindle motor when the replaceable recording medium is inserted and a medium supporting part has a mechanical tolerance. Moreover, the disk surface of the recording medium is physically uneven and distorted.
Thus, the recording medium is tilted at an angle to an optical head. Disadvantages known as tilt and skew occur.
FIG. 1 is a diagram showing a state of reading from a recording medium. FIG. 2 is a graph showing one distance between an optical head and the recording medium and another distance between an electromagnet and the recording medium, in correspondence with a rotation degree of the recording medium.
In FIG. 1, the surface of the recording medium 102 is not perpendicular but is tilted with respect to a spindle shaft 101 of a spindle motor 100.
In this state, when the recording medium 102 is rotated by the spindle motor 100 and a beam spot 105 from the optical head 103 scans on a track 104, a distance between the optical head 103 and the surface of the recording medium 102 is depicted by a sine curve with solid line shown in FIG. 2 in correspondence with the rotation degree.
On the other hand, the electromagnet 106 and the optical head 103 face each other and the recording medium 102 is provided between the electromagnet 106 and the optical head 103. Thus, a distance between the electromagnet 106 and the surface of the recording medium 102 is depicted by a cosine curve with dotted line in correspondence with the rotation degree.
Further, FIG. 3 is a diagram showing another state of reading from a recording medium. FIG. 4 is a graph showing a characteristic of a tilt of the recording medium with respect to the optical head in the state shown in FIG. 3. FIG. 5 is a graph showing a distance between the recording medium and the electromagnet in the state shown in FIG. 3.
FIG. 3 shows a state in which a recording medium 110 is a distorted plate. In this state, when the optical head 103 moves in an arrow A2 direction, that is, from the inner side to the outer side, a vertical distance between the optical head 103 and the surface of the recording medium decreases as shown in FIG. 4. Also, as shown in FIG. 5, the vertical distance between the electromagnet 106 and the surface of the recording medium 110 is greater on the outer side and less on the inner side.
Accordingly, in the state in FIG. 1 or FIG. 3, an incident beam emitted from the optical head can not be perpendicular with respect to the recording medium. Thus, the shape of the laser spot is distorted. Consequently, an expected laser power for reading or writing can not be achieved. In addition, an external magnetic field applied to the recording medium 110 is changed by a distance between the recording medium 110 and the electromagnet 106. Thus, an expected magnetic field strength can not be achieved.
In a case in which the expected laser power is not achieved, an unexpected laser power does not affect the quality of reading or writing when a recording density such as a track per inch (TPI) or a bit per inch (BPI) is low. However, when the recording density is high, an error rate is increased and can not be ignored.
Also, in a case in which the expected external magnetic field strength is not achieved, an unexpected magnetic field strength does not affect the quality of reading or writing when the recording density is low. However, when the recording density is high, the error rate is increased and can not be ignored.
Therefore, a method is provided to correct the tilt and skew of the recording medium 102 or 110 by adjusting a tilt of the spindle motor 100.
In the method in which the tilt and skew of the recording medium 102 or 110 is corrected by adjusting the spindle motor 100, it is required to provide a mechanism for controlling the inclination of the spindle motor 100 and a sufficient space for the mechanism. Disadvantageously, when the spindle motor 100 is mechanically adjusted, it is difficult to carry out the adjustment at a high rotation speed.
It is a general object of the present invention to provide an information storage apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an information storage apparatus in which a proper external magnetic field strength is obtained by controlling the external magnetic field strength, instead of adjusting a tilt of a recording medium,
The above objects of the present invention are achieved by an information storage apparatus for emitting a light beam to a recording medium and recording information on the recording medium by applying an external magnetic field to a position illuminated by the light beam, including: an external magnetic field control part controlling an external magnetic field strength based on the illuminated position on the recording medium.
According to the present invention, the external magnetic field strength is controlled based on the illuminated position on the recording medium. Therefore, it is possible to properly read or write data from or to the recording medium even if the recording medium is distorted or tilted.
Also, the above objects of the present invention are achieved by a method for emitting a light beam to a recording medium and recording information on the recording medium by applying an external magnetic field to a position illuminated by the light beam, including the step of: controlling an external magnetic field strength based on the illuminated position on the recording medium.
According to the present invention, the method can be provided to properly read or write data from or to the recording medium even if the recording medium is distorted or tilted.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.